In the case of fossil-fueled power stations for generation of electrical energy on a large scale, a large amount of off-gas, which contains carbon dioxide, is produced by the combustion of a fossil fuel. In addition to carbon dioxide, the off-gas contains further components, such as the gases nitrogen, sulfur dioxide, nitrogen oxides and steam, as well as solid particles, dusts and soot. In relatively modern or modernized power stations, the solid components are already separated, the sulfur oxides are already separated, and the nitrogen oxides are already removed catalytically. Until now, the carbon dioxide contained in the off-gas has been allowed to escape with the off-gas into the atmosphere. The carbon dioxide accumulating in the atmosphere is preventing heat from being radiated from our planet and, as a result of the so-called greenhouse effect, is promoting an increase in the surface temperature of our planet. Carbon dioxide can be separated from the off-gas, in order to achieve a reduction in the carbon-dioxide emission from fossil-fueled power stations.
Various methods are known for separation of carbon dioxide from a gas mixture, in particular from the chemical industry. The absorption/desorption method is known in particular for separation of carbon dioxide from an off-gas following a combustion process (post-combustion CO2 separation).
The separation of carbon dioxide using the absorption/desorption method is carried out using a washing agent. In a traditional absorption/desorption process, the off-gas is brought into contact with a selective solvent, as the washing agent, in an absorption column. In this case, the carbon dioxide is absorbed by means of a chemical or physical process. The cleaned off-gas leaves the absorption column for further processing or extraction. The solvent loaded with carbon dioxide is passed into a desorption column in order to separate the carbon dioxide and to regenerate the solvent. The separation process in the desorption column can be carried out thermally. In this case, a gas/vapor mixture composed of gaseous carbon dioxide and vaporized solvent is forced out of the loaded solvent. The vaporized solvent is then separated from the gaseous carbon dioxide. The carbon dioxide can now be compressed, cooled and liquefied in a plurality of stages. The carbon dioxide can then be supplied to a storage depot or for further use, in the liquid or frozen state. The regenerated solvent is passed back to the absorber column, where it can once again absorb carbon dioxide from the off-gas which contains carbon dioxide.
The main problem with the existing methods for separation of carbon dioxide from a gas mixture on a large scale is, in particular, very high energy consumption which, inter alia, is required in the form of heat energy for the desorption process.
One general disadvantage of known separation processes for carbon dioxide from an off-gas, with these processes being connected in or after a power-station process, is, in particular, the influence of the separation method on the power-station process, since it makes the efficiency considerably worse. The deterioration in the efficiency occurs because the energy for carrying out the carbon-dioxide separation process must be taken from the power-station process. The efficiency of a fossil-fueled power station with a carbon-dioxide separation apparatus is therefore considerably lower than that of one without a carbon-dioxide separation apparatus.